Q: Why do we see the Moon during the day but not the Sun at night?
Millie | Queens Village, New York
By definition, night is the time when our side of the Earth is facing away from the Sun. That explains why we can’t see the Sun at night. But why do we sometimes see the moon in the daytime? The Moon orbits the Earth roughly once each month. For half a month it is on Earth’s daytime side, and it is visible for a least part of nearly every day during that time, especially for us in the northern summer. The difference is that at night, even a sliver is easy to spot as long as it’s in our line of sight. So the Moon isn’t a feature specific to the night sky. If people think of it that way, that’s only because darkness makes the Moon much easier to observe. —R. Bruce Ward, retired science educator, Center for Astrophysics, Harvard & Smithsonian
Q: I still see the term “American Indian” in use, including in the title of a Smithsonian museum. Why not say “Native American” instead?
Dan Lau | Los Altos, California
Native people prefer to be identified with their own specific tribe or tribes. But when it comes to describing all of these nations with one term, there’s no consensus. Groups in Alaska like to be called “Alaskan Natives,” while those in Canada prefer the term “First Nations.” Some others in South America call themselves “AmerIndian.” Even though the term “Indian” originally came from a misunderstanding, many tribal people still prefer it over the alternatives. (Some point out that any person born in the Americas could be called a “Native American.”) I personally say “American Indian” because it is the language of the law between the tribal and federal governments. —Dennis Zotigh, cultural specialist, National Museum of the American Indian
Q: We own a christening gown that has been used by family members since about 1880. What’s the best way to preserve it?
Robert Metzger | Raymond, Mississippi
Your christening gown needs to be stored in a clean, cool, dry and dark space to prevent light exposure and attacks from insects or mold. Please avoid the basement or attic. You should also place your gown in an acid-free archival box to protect against dust, dirt and pollutants. Use acid-free tissue to cover the gown and pad the folds to prevent creases and further splitting. If you’d like more specific guidance from an expert, you can go to Culturalheritage.org and find a textile conservator near you. —Sunae Park Evans, senior costume conservator, National Museum of American History
Q: Why don’t marine animals die from drinking seawater the way people do?
Rob Loughridge | Honolulu
Animals such as seabirds, sea turtles and fish have adaptations that allow them to remove the salt from their systems. In non-marine animals, however, drinking seawater leads to dehydration, and ultimately death, because the kidneys have to use even more water to flush out seawater’s excess salt. Marine mammals avoid this fate by getting water through their food. Some also have special adaptations in their kidneys to help them purge salt more efficiently. Ingesting a bit of saltwater through an accidental gulp produces no harmful effects. —Emily Frost, Ocean Portal Managing Editor, National Museum of Natural History